Fluid pressure generating means

ABSTRACT

A fluid pressure generating means ( 10 ) for a heart assist device having blood pumping means. The pressure generating means ( 10 ) includes a housing ( 11 ), defining an interior volume ( 18 ), and having a substantially rigid first housing portion ( 12 ), a substantially rigid second housing portion ( 14 ), a flexible third housing portion ( 16 ) extending between the first ( 12 ) and second ( 14 ) housing portions and an inlet/outlet port ( 15 ) adapted for fluid communication with the blood pumping means. The pressure generating means ( 10 ) also includes a fluid filling the housing and a motor ( 20 ) disposed within the housing ( 11 ) and connected between the first ( 12 ) and second ( 14 ) housing portions. Actuation of the motor ( 20 ) moves the first ( 12 ) and second ( 14 ) housing portions relative to one another to generate fluid pressure changes at the inlet/outlet port ( 15 ). A related heart assist device and method for the treatment of congestive heart failure, myocardial ischemia and like conditions are also disclosed.

FIELD OF THE INVENTION

The present invention relates to a fluid pressure generating means foruse with a heart assist device.

BACKGROUND OF THE INVENTION

The applicant's international PCT patent application no. PCT/AU00/00654(International publication no. WO 00/76288) entitled “Heart AssistDevices, Systems and Methods” (“the PCT application”) discloses numerousembodiments of a novel heart assist device adapted for implantation intoa patient. Broadly speaking, the disclosed heart assist devices include:an aortic compression means adapted, when actuated, to compress an aortaof a patient; a fluid reservoir; and a fluid pressure generating meansadapted to pump fluid from the fluid reservoir to the aortic compressionmeans so as to actuate the aortic compression means in counterpulsationwith the patient's heart. The relevant portions of the PCT applicationare incorporated herein by cross-reference.

It is a first object of the present invention to provide improved fluidpressure generating means suitable for use with the aortic compressionmeans described in the PCT application. It is a second object to providea fluid pressure generating means which may be placed more convenientlyinto the body of a patient.

SUMMARY OF THE INVENTION

Accordingly, in a first aspect, the present invention provides a fluidpressure generating means for a heart assist device having blood pumpingmeans, the pressure generating means including:

a housing, defining an interior volume, and having a substantially rigidfirst housing portion, a substantially rigid second housing portion, aflexible third housing portion extending between the first and secondhousing portions and an inlet/outlet port adapted for fluidcommunication with the blood pumping means;

a fluid filling the housing; and

a motor or other actuator means disposed within the housing andconnected between the first and second housing portions,

wherein actuation of the motor or other actuator means moves the firstand second housing portions relative to one another to generate fluidpressure changes at the inlet/outlet port.

In one preferred form, the third housing portion has an outer edge aboutits periphery and inner edge about an opening and is joined along theouter and the inner edge to the first and second housing portionsrespectively.

In another preferred form, the third housing portion is connected toonly one of the first and second housing portions and abuts against theother of the first and second housing portions.

The blood pumping means is preferably adapted to displace blood in theaorta, more specifically the ascending aorta, and preferably bycompressing or deforming the aorta of a patient in counter-pulsationwith the patient's heart. More preferably, the blood pumping means isadapted to displace blood from the ascending aorta of the patient. In analternative arrangement, the fluid pressure generating means can be usedto drive a conventional left ventricular assist device or anextra-ventricular co-pulsation heart compression device. In such anarrangement suitable valves are used to ensure the correct direction ofblood flow through a pumping chamber driven by the fluid pressuregenerating means.

In a further preferred form, one of the first and second housingportions is moveable and the other of the first and second housingportions is fixed, the moveable housing portion being exposed to theoutside of the heart assist device and adapted to interface with thelung of a patient.

In a yet further preferred form, one of the first and second housingportions is moveable and the other of the first and second housingportions is fixed, the moveable housing portion not being exposed to theoutside of the heart assist device and the device including a flexiblecompliance chamber. The compliance chamber is desirably in contact withthe lung of a patient.

The actuating means desirably includes a nut coupled to one of the firstand second housing portions and a threaded shaft coupled to the other ofthe first and second housing portions, the threaded shaft and the nutbeing threadedly engaged and the motor being adapted to rotate the nutrelative to the threaded shaft. In one arrangement, the nut is connectedto the moveable one of the first and second housing portions and thethreaded shaft is connected to the fixed one of the first and secondhousing portions. In another arrangement, the threaded shaft isconnected to the moveable one of the first and second housing portionsand the nut is connected to the fixed one of the first and secondhousing portions.

In an embodiment, the outflow of the fluid from the inlet/outlet port isaxial to the housing. In another embodiment, the outflow of the fluidfrom the inlet/outlet port is radial to the housing. In a furtherembodiment, the outflow of the fluid from the inlet/outlet port istangential to the housing.

A surface of the device is preferably curved to fit snugly with thechest wall and/or mediastinum and/or diaphragm of a patient.

The blood pumping means is preferably in the form of a fluid operatedcuff adapted to surround the patient's aorta.

The fluid filling the housing is preferably a liquid. The liquid ispreferably an oil or saline. The oil is preferably a silicone oil anddesirably has viscosity between 10 and 100 centistokes, most desirablybetween 10 and 30 centistokes.

In a second aspect, the present invention provides a heart assist deviceincluding:

a blood pumping means adapted, when actuated, to cause or assist themovement of blood around the patient's vasculature;

a fluid reservoir;

a fluid pressure generating means adapted to pump fluid from the fluidreservoir to the blood pumping means; and

a housing containing both the fluid reservoir and the fluid pressuregenerating means that is so shaped and dimensioned as to be adapted tolie in the plueral cavity, adjacent to the lung, when the blood pumpingmeans is functionally positioned within the patient.

In a third aspect, the present invention provides a method for thetreatment of congestive heart failure, myocardial ischemia and likeconditions, the method comprising:

inserting into the plueral cavity within the chest (preferably the rightchest) of a patient, and adjacent to the lung, a housing containing afluid reservoir and a fluid pressure generating means adapted to pumpfluid from the fluid reservoir to blood pumping means functionallyplaced in the patient so as to cause or assist the movement of bloodaround the patient's vasculature.

Until now most implanted heart assist devices have been placed in theabdominal cavity of a patient. This is disadvantageous as it complicatesthe surgical procedure and is unduly invasive for the patient. The fewproposals for placement of such a device in the chest cavity haveproposed the placement of the device against the inside of the chestwall so that the device can be wired to the ribs of the patient. It wasapparently felt that this was necessary to support the weight of thedevice and to prevent it from moving around in the patient. The presentinventors have found that the device may be placed against themediastinum directly adjacent the patient's heart and attached tosurrounding soft tissue. The device will thus lie in the plueral cavity,adjacent to the lung. The device preferably lies in a sagittal planewithin the patient's body. Desirably, the device will not touch theinside surface of the chest wall at all. This placement will reduce painfor the patient and make placement of the device easier for the surgeonimplanting the device.

Preferably, the blood pumping means referred to in the above method isadapted to compress the aorta of a patient in counter-pulsation with thepatient's heart. More preferably, the blood pumping means is adapted tocompress the ascending aorta of the patient.

In a fourth aspect, the present invention provides a heart assist deviceincluding:

a blood pumping means adapted, when actuated, to cause or assist themovement of blood around the patient's vasculature;

a fluid reservoir; and

a fluid pressure generating means driven by an electric motor andadapted to pump a liquid from the fluid reservoir to the blood pumpingmeans;

the electric motor having a cogging torque which is sufficiently lowthat the natural systolic blood pressure of the patient is sufficient tocause liquid in the blood pumping means to be returned to the fluidreservoir in the event that the electric motor stops.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will now be described, by way ofexamples only, with reference to the accompanying drawings in which:

FIG. 1 is a schematic longitudinal sectional view of a first embodimentof a fluid pressure generating means according to the invention;

FIG. 2 is a schematic longitudinal sectional view of a second embodimentof a fluid pressure generating means according to the invention;

FIG. 3 is a schematic longitudinal sectional view of a third embodimentof a fluid pressure generating means according to the inventionconnected to a heart assist device;

FIG. 4 a is a perspective view of a fourth embodiment of a fluidpressure generating means according to the invention;

FIG. 4 b is an underside perspective view of a housing portion of thefluid pressure generating means shown in FIG. 4 a;

FIG. 4 c is a schematic longitudinal sectional view of the fluidpressure generating means shown in FIG. 4 a; and

FIG. 5 is a schematic longitudinal sectional view of a fifth embodimentof a heart assist device according to the invention;

FIG. 6 is a perspective view of the device shown in FIG. 5; and

FIG. 7 is a perspective view of the device shown in FIG. 6 afterimplantation into the pleural cavity, medial to the lung, of a patient.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring firstly to FIG. 1, there is shown a schematic longitudinalsectional view of a first embodiment of a fluid pressure generatingmeans according to the invention, in the form of pump 10. The pump 10includes a housing, indicated generally by the reference numeral 11,comprising a substantially rigid bell-shaped first housing portion 12, asubstantially rigid flat circular second housing portion 14 and aflexible third housing portion or membrane 16.

The first, second and third housing portions 12, 14 and 16 togetherdefine an external boundary of the housing 11 around an interior volumedenoted 18, which is filled with a silicone oil. The second housingportion 12 itself formed from a cone-shaped portion 12 a which issealingly connected, after assembly of the pump 10, to a cylindricalportion 12 b.

The cone-shaped portion 12 a also includes an inlet/outlet port 15,which is connected in fluid communication with an aortic compressionmeans or blood pumping means (not shown) by a conduit 17.

The membrane 16 is substantially annular in configuration and hasenlarged inner and outer edges 16 a and 16 b which are sealinglyreceived in corresponding circumferential recesses 12 c and 14 aprovided in the first and second housing portions 12 and 14respectively.

The pump 10 also includes an electric motor, indicated generally by thereference numeral 20, within the interior volume 18 of the housing 11.The motor includes a rotor 21, rotor laminations 22, magnets 24, stator25, stator laminations 26, end windings 28 and bearings 30.

The stator 25 is fixed to the housing portion 12 a by a number of screws30 (only one shown). The rotor 21 is fixed to a nut 32, which is itselfthreadedly engaged with a threaded shaft 34 through ball bearings (notshown). The shaft 34 is fixed to the housing portion 14 by screw 36. Thestator 25 also includes a number of guide journals 38 (only one shown)through which are guided a corresponding number of shafts 40 that dependfrom the housing portion 14.

Power and control signals are fed to the motor 20 through lines 42 and44 respectively.

The operation of the pump 10 will now be described. Energising the motor20 to rotate in a first direction rotates the nut 32 relative to thethreaded shaft 34 which causes the threaded shaft 34 to move in adirection parallel to its longitudinal axis in a first directionindicated by arrow 46. FIG. 1 shows the shaft 34 at the end of itstravel in this direction and after driving the housing portion 14 awayfrom the housing portion 12 to increase the interior volume 18 and causea suction or negative pressure at the inlet/outlet port 15. This suctionactively deflates the aortic compression means (not shown).

Energising the motor to rotate in the opposite direction causes thethreaded shaft 34 to move parallel to the longitudinal axis in theopposite direction indicated by arrow 48 and draw the portion 14 towardsthe housing portion 12. The end limit of travel in this direction isindicated in phantom in FIG. 1 and, with reference to which it should benoted that, the guide shaft 40 abuts the inner surface of the housingportion 12 a at the limit of its travel at recess 50. Drawing theflexible portion 14 towards the housing portion 12 reduces the interiorvolume 18 which causes a positive pressure at the inlet/outlet port 15and drives fluid from the interior volume 18 to inflate the aorticcompression means.

The motor 20 is actuated cyclicly in this manner in counterpulsationwith the patient's heart in response to signals received from an ECGmonitor or systemic arterial pressure, as disclosed in the PCTapplication.

Referring now to FIG. 2, there is shown a schematic longitudinalsectional view of a second embodiment of a fluid pressure generatingmeans according to the invention, in the form of pump 60. The pump 60 issimilar to the pump 10 shown in FIG. 1 and like features are indicatedwith like reference numerals. Differences between the pumps 10 and 60are described in detail below.

Firstly, the housing portion 12 a of the pump 60 includes an opening 62sealed by a second flexible membrane 64 which forms a compliance chamber65. The chamber 65 is in fluid communication with the interior volume18. Secondly, the inlet/outlet port 15 is provided in a further housingportion 66 which is sealed with respect to the side of the secondhousing portions 14 and third housing portion 16 that is remote themotor 20. The housing portion 66 creates, in conjunction with thehousing portions 14 and 16, a second interior volume 68 in fluidcommunication with the aortic compression means or blood pumping means(not shown) via conduit 17.

The operation of the pump 60 is similar to that as described withreference to the pump 10 with the exception that the movement of thehousing portion 14 causes volume changes in the second interior volume68 which in turn inflates and deflates the aortic compression means. Themovement of the housing portion 14 also causes fluid movement in thepart of the interior volume 18 within the first, second and thirdhousing portions 12, 14 and 16 and these changes cause an identicalvolume change in the interior of the compliance chamber 65, which isshown having a decreased volume in response to the compression meansbeing inflated. The chamber 65 will have an increased volume in responseto the compression means being deflated, as is shown in phantom.

As the interior volumes 18 and 68 are maintained sealed from one anotherby the second and third housing portions 14 and 16, the pump 60 can beconfigured to use different fluids in each of the interior volumes 18and 60, as desired. For example, a saline solution can be used in theinterior volume 68 and a lubricating oil can be used in the interiorvolume 18 which contains the motor 20.

FIG. 3 is a schematic cross sectional side view of a third embodiment ofa fluid pressure generating means according to the invention, in theform of pump 80. The pump 80 is shown connected to an aortic compressionmeans or blood pumping means in the form of cuff 82. The pump 80 issimilar to the pump 60 described in relation to FIG. 2 and likereference numerals will be used to indicate like features. Differencesbetween the pumps 60 and 80 are described in detail below.

Firstly, the pump 80 has a first external substantially rigidcylindrical housing portion 84, a pair of second internal substantiallyrigid housing portions 86 a and 86 b and a third substantially flexiblehousing portion 88. The latter seals an end of the first housing portion84. The pump 80 also includes a second flexible housing portion 90 whichseals the other end of the second housing portion 84 and forms acompliance chamber 92. Secondly, the second housing portion 86 and thethird flexible housing portion 88 abut, but are not connected, to eachother.

The operation of the pump 80 is similar to that described with referenceto pump 60 in that the motor 20 is energised to reciprocally drive thethreaded shaft 34 and thus the second housing portion 86 a in directions46 and 48 parallel to the longitudinal axis of the threaded shaft 34.

FIG. 3 shows the pump 80 in a position after movement of the secondhousing portion 86 a in the direction 46 and driving fluid from thesecond interior volume 68 into the cuff 82 to inflate same. In thisposition, the second membrane of 64 is drawn into the interior of thesecond housing portion 84 to maintain the interior volume 18 constant.Driving the threaded shaft 34 in the opposite direction 48 results inthe housing portion 86 b forcing the membrane 64 to the position shownin phantom which is external the second housing portion 84. This alsoresults in the third housing portion 88 being drawn to the position alsoshown in phantom to maintain the interior volume 18 constant. Aspreviously described in relation to pump 60, when the third housingportion 86 is in this position fluid is drawn into the second interiorvolume 68 from the cuff 82 to deflate same.

FIGS. 4A to 4C show a fourth embodiment of a fluid pressure generatingmeans according to the invention, in the form of pump 100. The pump 100is similar to the pump 10 shown in FIG. 1 and like components have beenreferred to with like reference numerals. However, the pump 100 has beendesigned to be as thin as possible (dimensions: 82 mm long; 60 mm wide;and 45 mm deep) in order to allow positioning in a patient's chest incontact with the mediastinum adjacent the heart. The pump 100 is placedwith the planar housing portion 14 lying in a sagittal plane and as withthe edge of the housing 100 clear of the inside surface of the chestwall. This orientation is chosen so as to minimise pain and trauma tothe patient and also minimise the length of conduit required between thepump 100 and the aortic compression means (not shown). This positioningalso assists the surgeon in placing the device.

Referring finally to FIGS. 5 to 7, there is shown a schematiclongitudinal sectional view of a fifth embodiment of a fluid pressuregenerating means according to the invention in the form of pump 120. Thepump 120 is shown connected to an aortic compression means or bloodpumping means in the form of cuff 122. The construction and operation ofthe pump 120 is similar to die pump 10 shown in FIG. 1 and like featuresare indicated with like reference numerals. The size of the pump 120 issimilar to the pump 100 shown in FIGS. 4A to 4C, except it is more ovateand has flattened sides (See FIG. 6). The ovate form of the pump 120 andthe positioning of the cuff 122 nearer one end allows the device to beplaced in the plural cavity, medial to the lung, and lying in a sagittalplane within the patient's body, as is shown in FIG. 7. The pump 120does not touch the inside surface of the patient's chest wall in thisposition. FIG. 7 also shows an external battery pack 123 which powersthe pump 120.

The main differences between the pumps 10 and 120 are as follows.Firstly, the flexible third housing portion 16 is sealingly connectedabout its outer edge 16 b to the substantially rigid ovate cup-shapedfirst housing portion 12. The connection and sealing is achieved by asealing rim 124 on the third portion 16 being snugly received in anannular recess 126 on the first portion 12. Secondly, the substantiallyrigid flat ovate second housing portion 14 is received within acorresponding recess in the third portion 16, on the interior side ofthe third portion 16, and is thus within the interior volume 18.

FIG. 5 shows the pump 120 in a position after movement of the secondhousing portion 14 in the direction 46, which draws fluid into theinterior volume 18 from the cuff 122 and deflates same. Driving thethreaded shaft 34 in the opposite direction 48 forces the second housingportion 14 towards the motor 20 (see the position of the shaft 34 shownin phantom). As previously described, when this occurs, fluid is forcedfrom the interior volume 18 into the cuff 82 to inflate same.

An advantage of the preferred embodiments of fluid pressure generatingmeans described above is the liquid surrounding the motor is used bothas a driving fluid to inflate/deflate the compressions (either directlyas per the embodiments of FIGS. 1 and 4 or indirectly as per theembodiments of FIGS. 2 and 3) and as a cooling/lubricating/heatexchanging fluid. The liquid also dampens sound made by the pumpmechanism. This simplifies the construction, and minimises the size, ofthe fluid pressure generating means.

Whilst the fluid pressure generating means will normally actively driveboth the inflation and deflation of the aortic compression means, themotor is preferably designed so that the cogging torque of the motor issufficiently low that the natural systolic blood pressure of the patientis sufficient to deflate the cuff. If the motor is inactivated for anyreason with the cuff in an inflated condition (and thus with the aortapartially occluded), this arrangement means that the natural systolicblood pressure will deflate the cuff by pushing fluid from the cuff intothe housing and passively driving the second housing portion away fromthe motor.

It will be appreciated by person skilled in the art that numerousvariations and/or modifications can be made to the invention as shown inthe specific embodiments without departing from the spirit or scope ofinvention as broadly described. For example, the embodiments of theinvention are not restricted for use with the embodiments of the heartassist device shown in the PCT application. The specific embodimentsare, therefore, to be considered in all respects as illustrative and notrestrictive.

1. A fluid pressure generating device for a heart assist device having ablood pumping means, the pressure generating device including: ahousing, defining an interior volume, and having a substantially rigidfirst housing portion, a substantially rigid second housing portion, aflexible third housing portion extending between the first and secondhousing portions and an inlet/outlet port connected to one of saidhousings and adapted for fluid communication with the blood pumpingmeans, the third housing has an outer surface about its periphery, aninner surface facing the interior of the first and second housing and isjoined along the outer edge and the inner edge to the first and secondhousing portions respectively; a fluid filling the interior volume ofthe housing; and a motor disposed within the interior volume of thehousing and connected between the first and second housing portions,wherein actuation of the motor moves the first and second housingportions relative to one another to generate fluid pressure changes atthe inlet/outlet port.
 2. A fluid pressure generating device for a heartassist device having a blood pumping means, the pressure generatingdevice including: a housing, defining an interior volume, and having asubstantially rigid first housing portion, a substantially rigid secondhousing portion, a flexible third housing portion extending between thefirst and second housing portions and an inlet/outlet port connected toone of said housings and adapted for fluid communication with the bloodpumping means, wherein one of the first and second housing portions ismoveable and the other of the first and second housing portions isfixed, the moveable housing portion being exposed to the outside of theheart assist device and adapted to interface with the lung of a patient;a fluid filling the interior volume of the housing; and a motor disposedwithin the interior volume of the housing and connected between thefirst and second housing portions, wherein actuation of the motor movesthe first and second housing portions relative to one another togenerate fluid pressure changes at the inlet/outlet port.
 3. A fluidpressure generating device for a heart assist device having a bloodpumping means, the pressure generating device including: a housing,defining an interior volume, and having a substantially rigid firsthousing portion, a substantially rigid second housing portion, aflexible third housing portion extending between the first and secondhousing portions and an inlet/outlet port connected to one of saidhousings and adapted for fluid communication with the blood pumpingmeans, wherein one of the first and second housing portions is moveableand the other of the first and second housing portions is fixed, themoveable housing portion being exposed to the outside of the heartassist device and the device including a flexible compliance chamber;wherein the compliance chamber is adapted to be in contact with the lungof a patient; a fluid filling the interior volume of the housing; and amotor disposed within the interior volume of the housing and connectedbetween the first and second housing portions, wherein actuation of themotor moves the first and second housing portions relative to oneanother to generate fluid pressure changes at the inlet/outlet port.